This paper will discuss the use of psychoacoustic evaluation as a tool for optimization of the soundscape simulator developed in the Listen project. The listen project is a three-year research project focused around developing a demonstrator, which auralizes the sound environment produced by road and railway traffic. The resolution of the parameter space of the simulator heavily influences the performance of the simulator. The perceptual resolution of the parameter space is investigated and the resolution is adjusted accordingly. The most important parameter is velocity. Adjustments of the resolution of this parameter alone gives a 60% reduction of the usage of memory